Coil construction



July 2, 1929. BRQSCOTT 1.719.241

COIL cousmucnon f Fil ed Feb. 19, 1926 INVENTOR Patented July 2, 1929.

UNITED STATES PATENT o -FICE.

I BEVERLEY RANDOLPH SCOTT, OF WOODLYNNE, NEW JERSEY, ASSIGFTOR 'I'O THEHAM- MARLUND MANUFACTURING COMPANY, INCORPORATED, A CORPORATION'OF NEWYORK.

COIL CONS Application filed February My invention relates particularlyto-wire Y coils used for various purposes such as electric inductances.

One object is to provide a coil -of high inductance value and lowdielectric loss. relatively low resistance and small distributedcapacity. I 1

Another object is to provide a coil which can be readily handled andmounted. 7

Another object is to provide a coil having permanent and uniformcharacteristics.

I have solved the problem by the simple expedient of winding a coil upona very thin layer of dielectric material to Which it is permanentlyanchored. The method of manufacture which will be hereinafter de scribedmakes it possible to maintain any desired spacing of the various turns.

Fig. 1 is a side view of the coil made according to my invention.

Fig. 2 is an end view of the same.

Fig. 3 is a perspective view of a mandrel showing one method of applyingthe dielectric.

Figs. at and 5 are diagrammatic end views of two other arrangements ofthe supporting dielectric.

Fig. 6 is a diagrammatic end view of a coil of angular cross-sectionsupported on two strips of dielectric.

Fig. 7 is an enlarged longitudinal sectional view showing a fragment ofa coil in process of manufacture.

Fig. 8 is a similar sectional view showing the same after the wirehasbeen permanently secured in place. 7

The foundation 10 of the coil is made up of one or more strips of amaterial such as a nitrocellulose composition, for instance, celluloidor pyroxylin.

The conductor 11 is covered with insulating material 12 such as silk orcotton fibre.

In making the coil I preferably employ a mandrel 18 made up of a seriesof sections such as shown in Fig. 3 and provided with a tapered shaft 14capable of expanding and su imorting the mandrel. According to thepreferred method of manufacture, a very thin sheet of celluloid, sayfive-thousandths of an inch thick, is wrapped around the mandrel and theedges of the sheet overlapped, as indicated in Fig. 3, and stucktogether by the simple expedient of applying a suitable solvent, such asethyl-acetate TBUCTION.

19, 1926. Serial No. 89,292.

to the material. along the line of overlap,

the edges of the sheet to be drawn together smoothly and pressedtogether immediately after the solvent is applied. I have found thatthis operation of cementing the edges together on the mandrel can bemost conven ently affected by the use of asphincter spring 15.Thisspring normally rests in a groove 16 in one endof the mandrel and,

is run alongthe surface of the celluloid as soon as the overlappingedges have been moistened with the solvent. Springs 16' hold the mandrelparts together. When the edges of the strip have been united on themandrel, the mandrel is expanded in the usual mannerby simply drivingthev shaft longitudinally. This places the celluloid tube under tension.The mandrel is then placed in a winding machine and thewire;

wound on it under tension. "This tension should remain substantiallyconstant throughout the winding operation and the feeding of the wireshould of course be at the proper rate to lay the wire with the desiredspacing between adjacent turns. When the coil has been wound, a suitablesolvent, such as ethyl-acetate is applied to the foundation between theadjacent turns of the wire, for instance, by means of a brush. Thissolvent penetrates the insulation of the wire and immediately softensthe surface of the foundation. The coil being under tension, as beforedescribed, of course tends to contract in diameter and thus sinks verslightly into the softened surface of the co luloid or the like. Thechange in condition before and after the application of the solvent isshown bythe difference between the relative positions of the coil andfoundation as shown in Figs. 7 and 8. The mandrel may be contracted andwithdrawn as soon as the material has hardened, which requires only afew minutes. The finished coil will, however, continue to dry out forsome time, the length of time varying with the composition of thematerial, the nature of the solvent, and the amount applied, as well asthe atmospheric conditions. In drying out the coil shrinks lengthwise,sometimes as much as 10% and becomes corrugated in the longitudinalsection as shown in Fig. 8. These corrugations remain permanent and tendto hold the coils in position even if they become loosened from thecelluloid.

It is obvious that the coil may be wound at any length desired forspecial purposes. The method of manufacture lends itself particularly tothe production of long tubes which can be readily cut up into suchlengths as may be desired.

In the manufacture of these tubes, particularly in small sizes, there issometimes a tendency for the tube to warp when made as above described,due-to the overlapped joint along one edge. This can be readily avoided,however, by using two strips, such as 20 and 21, as shown in Fig. 4, sothat there will be oppositely disposed joints which will offset eachother in the shrinking process.

It should also be understood that any number of foundation strips may beused and that these strips may be spaced apart as shown for instance inFig. 5. Here I have shown four strips 23 with spaces 24 between them. Acoil wound in this manner has an added advantage of reducing thedielectric material to a minimum.

The forms shown in Figs. 5 and 6 are specifically claimed in myapplication #209,277, filed J'uly'29, 1927. I

' Although the coil is preferably circular in cross-section, it shouldbe understood that certain features of the invention'are applicable tocoils of other cross-sections, for instance, in Fig. 6, I have shown asquare coil wound on two strips 25 on opposite sides. This would, ofcourse, leave the wires 26 on the other sides spaced apart withoutsupports except at the edges of the strips 25.

Coils wound according to my invention may be used for various purposes,such, for instance, as radio frequency variable couplers, antennacouplers, interstage couplers, neutrodyne coils, short wave coils, etc.

The method of forming coils according to my invention is claimed in myPatent- #1,643,998, dated Oct. 4, 1927.

I claim:

tubular foundation of thin material such as sheetcelluloid ofsubstantlally uniform thickness, and a helix 01 wire cement-ed in theouter surface of the'foundation, the founda- I, t1on being corrugatedand the turns of the wire helix being cemented in the grooves of thecorrugations.

2. A coil comprising a foundation sheet of thin celluloid-like materialhaving its 4.

BEVERLEY RANDOLPH SCOTT.

I I 1. A self supporting coil comprising a'

